The present invention relates to an organopolysiloxane composition or, more particularly, to an organopolysiloxane composition curable by reacting with atmospheric moisture and by irradiating with ultraviolet light and useful as an adhesive or as a sealing agent.
Various kinds of curable organopolysiloxane compositions are known in the prior art including so-called room temperature-curable compositions having stability under a hermetically sealed condition but curable when exposed to the atmosphere containing moisture to be converted into a rubbery elastomer and ultraviolet-curable compositions having stability in dark but curable when irradiated with ultraviolet light to be converted into a rubbery elastomer. A variety of commercial products are available of these types of curable organopolysiloxane compositions and are used in a variety of applications.
A problem in the moisture-curable organopolysiloxane compositions is that, since the curing velocity of the composition depends on the diffusion of water vapor through the surface, curing of the composition cannot be so rapid as to convert a surface layer of a certain thickness into a rubbery elastomer within a short length of time of, for example, a few seconds so that the curable organopolysiloxane composition of this type is not suitable for use as an adhesive or sealing agent which is required to exhibit the desired adhesive or sealing effect within a short time.
A problem in the ultraviolet-curable organopolysiloxane composition is, on the other hand, that, although the composition is rapidly cured in the portion under direct exposure to ultraviolet light, curing can hardly proceed in the shade without direct exposure to ultraviolet or in a colored composition excepting the very surface layer. In particular, ultraviolet light cannot reach the core of a thick body of the composition which is left uncured excepting the surface layer.
It has been previously proposed that the above mentioned problem in the ultraviolet-curable organopolysiloxane composition can be at least partly solved when the composition is prepared by compounding a diorganopolysiloxane terminated at both molecular chain ends with siloanolic hydroxy groups as the base ingredient with a vinylsilane compound having a silicon-bonded vinyl group and a hydrolyzable group or a partial hydrolysis product thereof and a mercapto-containing organosilane compound having at least two mercapto groups in a molecule in combination so that the composition can be cured in two ways of the condensation reaction of the hydrolyzable groups with the atmospheric moisture in the shade of the ultraviolet light and the ultraviolet-induced addition reaction between the vinyl groups and the mercapto groups in the portion under direct exposure to ultraviolet. The improvement in the curing behavior of the organopolysiloxane composition mentioned above is still insufficient presumably due to the limited number of the vinyl groups. When a substantial amount of vinyl groups are introduced into the organopolysiloxane as the pendant groups of the polymeric molecules with an object to further improve the curing behavior of the composition, disadvantages are caused in the cured silicone rubber product in respect of the decrease in the elongation as a rubber and increase in the hardness.